1. Field of the Invention
The present invention relates to a magneto-optic memory element to which a laser beam is impinged to record, read out or erase the information onto or from the magneto-optic memory element.
2. Description of the Prior Art
Recently, a magneto-optic memory element has been developed, which is used in an optical memory disc storing alterable information. The most effective magneto-optic memory element includes a recording medium made of an amorphous alloy thin-film consisting of a rare earth metal and a transition metal. Such a magneto-optic memory element is stable because the recording bit is not affected by the grain boundary, and a large size recording medium can be easily formed.
However, the conventional magneto-optic memory element including the amorphous alloy thin-film recording layer consisting of a rare earth metal and a transition metal does not demonstrate a satisfactory S/N ratio of the reproduced signal because sufficient photoelectro-magnetic effects (Kerr effect and Faraday effect) are not obtained.
To enhance the photoelectro-magnetic effect, the engineering group including the present inventors has developed a magneto-optic memory element which includes an amorphous alloy thin-film recording layer consisting of rare earth metal and transition metal sandwiched by a pair of transparent dielectric layers. The dielectric layer is generally made of SiO or SiO.sub.2. The pair of transparent dielectric layers function to effectively combine the Kerr effect and the Faraday effect so as to increase the Kerr rotation angle. However, in the above-mentioned element, there is a possibility that the amorphous alloy thin-film recording layer is damaged due to the oxidation caused by the SiO or SiO.sub.2 dielectric layer.
A typical element of the above construction is disclosed in copending U.S. patent application, "MAGNETO-OPTIC MEMORY DEVICE", Ser. No. 697,027 which is a continuation of Ser. No. 489,889, filed on Apr. 19, 1983 by Kenji OHTA, Akira TAKAHANSHI, Hiroyuki KATAYAMA, Junji HIROKANE and Hideyoshi YAMAOKA, and assigned to the same assignee as the present application. The corresponding European Patent Application was filed on Apr. 28, 1983 and assigned Application No. 83302419.3. The corresponding Canadian Patent Application is Ser. No. 427,088 filed on Apr. 29, 1983.